Swimming pools can be a hazard when left unattended. Some swimming pool monitoring systems sound an alarm when an unauthorized or accidental entry of an object or individual into a pool occurs. Some systems use water pressure measurement devices in conjunction with diaphragms to detect the pressure differential in the water due to movement of the water. Other systems use infrared or acoustic sensors to detect movement of the water. In some systems, an electronic circuit incorporating probes spaced apart above the water can detect a momentary splash. Other systems use a transmitter, for example, worn on a child to set off an alarm if the child enters the water.